The proposed research will continue our efforts to define the roles of the genetic elements which specify muscle assembly in the nematode Caenorhabditis elegans. The advances made in the past grant period both in our own work and elsewhere make available a variety of powerful approaches to isolate genes and to study their roles in C. elegans. We shall exploit this knowledge base to study critical aspects of thick and thin filament assembly and we shall continue roles in muscle development. The myosin heavy chain sequences which allow the initiation of myosin assembly and the proteins with which they interact in the assembly process will be defined. The genes unc-87, unc-82, and unc-89 will be analysed to determine if they encode either minor components which play important parts in thick filament, somehow direct its assembly. The proteins vinculin and capZ are likely to have a role in initiating thin filament formation and positioning thin filaments within the cell. Vinculin mutants will be used to determine with which proteins it interacts and to study specific mutations of the gene to learn more about functions of the molecule. The genes for the capZ subunits will be identified and combined molecular genetic approaches used to define its role. Four other genes, unc-60, unc-78, unc-94 and unc-95, likely to have important functions in thin filament assembly will be studied through molecular and genetic studies. Whether these genes encode proteins that become incorporated into the lattice or instead direct its assembly by modifying its components will be ascertained. A class of new, essential muscle genes has been defined in the past grant period. We will collect additional mutants of this class, and describe the phenotypes of members of the class in more detail. We will focus our attention on a small number of these genes for more detailed molecular and genetic studies. These genes may encode additional components of the myofilament lattice or involve other aspects of muscle development. We shall also clone the nematode dynein heavy chain gene and use a combined molecular and genetic approach to determine its role in cell division and cell morphogenesis during development. By defining the role of these genes and identifying yet new ones, we will begin to learn the principles by which the genome specifies muscle structure in development, not only in the nematode, but in all higher organisms.